wikiHow is a “wiki,” similar to Wikipedia, which means that many of our articles are co-written by multiple authors. To create this article, 13 people, some anonymous, worked to edit and improve it over time. This article has been viewed 10,064 times.
Learn more...

You're learning your single digit multiplications, but for some reason you keep getting stuck on that last tricky number: 9. Read on to learn how to tackle those single digits and leave everyone else in your dust!

Steps

Method 1 of 2:

Numbers Method

1

Remember that any number multiplied by 1 is the number itself. No matter how tricky 9 is, it can't escape the fact that 1x9 will always equal 9.

2

Start simple and work your way up. Don't try to multiply 9x9 before you learn 9x2 because it is a lot easier to think of math like a ladder. You should take each step to the top because if you try to skip steps you may just fall back and have to start over.

3

Subtract 1 from the single digit you've chosen to multiply time 9 (starting with 2). When you subtract one from your digit, you will have the first digit in the product. For example, when you want to know the product of 9x2, subtract 1 from 2 and you will know your answer starts with a 1.

4

Subtract the first digit of your answer from 9. If you subtract the first number in your product from 9 you will get the second number in your product. We found out the first number in the product of 9x2 is 1 by subtracting 1 from 2 and 9-1=8.

5

Put your numbers together. You found the first digit of your answer to be 1 and then your next to be 8. This means the product of 9x2 is 18.

Note that the sum of the digits always equals 9. Even with multiplying 9 by numbers higher than ten, if you add all the digits in a multiple of 9, and then add the digits again if there are more than one, and so on, you will always eventually end up with 9. For example, 9 x 15,873 is equal to 142,857. Add the digits of this number together, and get 27. Add the digits of this together and you will end up with 9.

6

Calculate other single multiplication problems with 9 with this method and you'll be able to solve them in your head in no time!

About This Article

wikiHow is a “wiki,” similar to Wikipedia, which means that many of our articles are co-written by multiple authors. To create this article, 13 people, some anonymous, worked to edit and improve it over time. This article has been viewed 10,064 times.